1. Field of the Invention
The present invention relates to a power transmission for automotive vehicles, and more particularly to a power transmission adapted for use in four-wheel drive vehicles.
2. Description of the Background
In Japanese Patent Early Publication No. 59-176120, there has been proposed a power transmission of this kind which comprises a trans-axle housing assembly formed therein with first, second and third compartments in open communication with each other, a change-speed gear transmission mounted within the first compartment to be applied with a drive power from a prime mover of the vehicle, a first transfer gear mechanism mounted within the second compartment to transfer an output drive power from the gear transmission to front wheel and rear wheel drive axles, and a second transfer gear mechanism mounted within the third compartment coaxially with the first transfer gear mechanism to transfer the drive power from the first transfer gear mechanism to the front wheel or rear wheel drive axles. In operation of the power transmission, lubricating oil stored in the comparments is picked up by respective gears of the gear transmission and transfer gear mechanisms and introduced to lubricate intermeshing and sliding portions of the gears.
In such a conventional power transmission as described above, the change-speed gear transmission is greater than the transfer gear mechanisms in the number of gears picking up the lubricating oil in the housing assembly. When the change-speed gear transmission starts to pick up the lubricating oil in operation of the power transmission, the level of lubricating oil in the first compartment gradually drops below the level of lubricating oil in the second and third compartments to cause flow of the lubricating oil into the first compartment from the second and third compartments. This results in insufficient lubrication of the first and second transfer gear mechanisms. If a sufficient amount of lubricating oil is stored in the three compartments to avoid the foregoing problen, there will occur large resistance during rotation of the gears in the gear mechanisms, resulting in loss of the drive power to be transmitted to the front and rear wheel drive alxes.